The invention concerns a stud welding head with a linear drive, a welding pin coupled with the linear drive, and a length measuring system that determines the position of the welding pin in the stud welding head.
Stud welding devices are, for example, used in the automobile industry to weld studs to the body of a car. The welding occurs in that a high voltage is applied between the studs secured in the welding head and the work piece and in that an electric arc is created. The positioning of the welding stud, namely the lifting of the welding stud and the creation of the electric arc as well as the subsequent dipping of the stud into the welding deposit should ensure that a consistently high weld quality is always achieved. Until now, only optoelectronic length- or distance-measuring systems have been used. These are sensitive with respect to the high welding currents and the corresponding magnetic fields. Strong magnetic fields can be created in stud welding heads also in the area of the linear drive, since the linear drives often operate according to the moving coil principle, i.e., they have current-carrying coils and permanent magnets. The optoelectronic length measuring systems are, however, temperamental with respect to dirt. Since a large number of welding jets are created in the area of the welding head and the environment is often very dusty, the previously used optoelectronic distance measuring systems are sealed in the welding head, which requires a lot of work.
The invention establishes a stud welding head, which is distinguished by its simple construction, and the length measuring system of which offers an even better resolution than the previously used length measuring system.
This is achieved for a stud welding head of the type named above in that the length measuring system is an electromagnetic length measuring system.
Practical experience has shown that electromagnetic length measuring systems, which are sensitive to dirt out of principle, are able to function in stud welding heads. This is completely surprising for an expert, since extremely high welding currents flow in the stud welding heads and, as a result, strong electromagnetic fields are created. As it turns out, resolutions, which are much higher than those in optoelectronic length measuring systems, can also be achieved in welding heads by electromagnetic length measuring systems.
In accordance with the preferred design, an incremental length measuring system with a magnetic band and a magnetic sensor is used, whereby the magnetic band is affixed to the welding pin. Due to the provision of a magnetic band, the effort required to fasten the band to the welding pin is low.
Moreover, the length measuring system can have an adjustable resolution in order to be able to adjust it based on conditions and requirements.
Alternatively, an inductive length measuring system is also used.
The preferred design uses a linear drive that functions according to the moving coil principle and has several series-connected coils, into which at least one permanent magnet extends, which is coupled with the welding pin. This type of linear drive has the advantage that it can achieve an exact positioning of the welding pin and is ideally supplemented with the electromagnetic length measuring system, which has a high resolution. Since this type of linear drive also creates extremely strong magnetic fields, it is all the more astonishing that an electromagnetic length or distance measuring system, in particular with the use of a magnetic band and an inductive magnetic sensor, functions highly accurately and is also stable in the long-term.